Yes, it sounds like for you with your very specific requirements and contacts that might be true. But you are using g+, just not much until people move across, that will increase. g+ also does everything twitter does, but with better filtering and no pointless length limits.
It's good that we have a choice. I use g+ and hangouts every day. I use facebook occasionally (usually in relation to running VT) and I've not re-installed whatsapp since I last wiped my phone (arond xmas). I don't think I've lost contact with anyone that matters and I have much better access to current information on things of interest to me.
As you say, horses for courses. And again, I didn't say "instead".
PS. I may have mixed you up with another poster when replying on the app. Sorry.